This invention relates to hydraulic door closer apparatus, and more particularly, to hydraulic door closer apparatus having temperature compensating features. In general, this invention relates to the general type of hydraulic door closer illustrated in U.S. Pat. No. 2,192,745, issued Mar. 5, 1940, to Hurd, in which a spring-urged hydraulic piston is arranged to bias a door to its closed position with appropriate hydraulic damping. Typically, in the use of apparatus of this sort, the force generated by a spring is transmitted between the door closer and, depending upon where the closer is mounted, either the door or door frame. For this purpose, it is conventional to provide a linkage consisting of a pair of links, coupled to the unit and to the door or door frame, as the case may be. In the Hurd patent to which reference is made above, a rack and pinion arrangement is used to convert the linear movement of the piston within the device to rotary motion of the linkage.
Upon opening of the door, the piston is driven by the pinion against the bias of a return spring and against fluid resistance provided by hydraulic circuitry within the device. The hydraulic circuitry can be adjusted to provide for variable cushioning or "back-check" effect as the door approaches the limits of its swing toward the open position. The movement of the door toward the closed position is accomplished by unloading of the return spring, the speed of closing being controlled by appropriate damping by the hydraulic circuitry.
The effect of temperature on the viscosity of oil and oil-based fluids such as hydraulic fluids is well-known. Typically, subjecting a hydraulic fluid to a decrease in temperature results in an increase in its viscosity, denoting a relative "stiffening" of the fluid to resist flow. In the context of door closer operation, this means that if a closer and its fluid are subjected to a reduction in operating temperature, movement of the piston will become more difficult, and hence, slower, reflecting the heightened resistance of the fluid to flow. In the extreme case, the closer might not work at all. At the other extreme, increased working temperature might cause sufficient "thinning" of the fluid to reduce or eliminate the damping effect of the closer. The closer may then close so abruptly as to result in damage to the door, door frame, or the closer itself.
For door closer installations which are subject to wide swings in temperature, such as for example, exterior doors subjected to seasonal changes in temperature, variations in ambient temperature can significantly affect the performance of the closer. Although closers are typically provided with manually adjustable means for selectively regulating fluid flow, it is inconvenient and impractical to continually manually adjust the closer to compensate for temperature changes.
It is, therefore, a principal object of this invention to provide a door closer in which temperature-compensating features are provided, so that wide swings in ambient temperature are automatically compensated for and the operating characteristics of the closer remain reasonably constant over a wide range of ambient temperatures.
Frequent door openings create friction which raises the oil temperature inside the closer. It is another general object of this invention to provide a door closer suitable for use in applications in which the closer itself is subjected to wide internal temperature swings.
The foregoing and other objects of this invention are realized, in a presently preferred form of the invention, by a door closer which has a housing containing a cylinder, a piston disposed in the cylinder, a linkage coupled to the piston for transmitting forces to and from the piston, and a hydraulic circuit for controlling movement of the piston in the cylinder. The hydraulic circuit in accordance with the invention is provided with one or more adjustable valve members each made up of multiple materials having different thermal properties, namely, a first portion of relatively dimensionally stable structural material, and a second portion made of a material whose dimensions are relatively highly responsive to temperature changes in the range of changes to which the closer is likely to be subjected. The second portion of the valve member is so designed and so disposed in operation that changes in the temperature to which it is subjected affect clearance between the second portion and a valve seat with which the valve member is associated. In effect, the dimensional changes in the second portion of the valve member induced by changes in temperature serve to restrict or enlarge a flow passage, thus altering the fluid resistance produced by the closer.